Mixed Legacy Collection - what's the best way to adapt?

So I have recently plunged into the M4/3 world with a GX7. I own a LOT of Pentax lenses both those with and without aperture rings. My first inclination was to get a PK adapter with the option to control aperture but then I wondered if there was a better way... . I have a few Nikon lenses and a few Canon FD lenses and I wondered if there was a good FD adapter that I could pair with a Nikon to FD and PK to FD adapter to give me a simple way to mate all three without buying three M4/3 adapters - plus if I later wanted to take the plunge and get an FD focal reducer I could fit any of these to it rather than having to buy multiple focal reducers.

Am I crazy? I assume for my DA Pentax Lenses I'll still need an adapter with aperture control (crude but better than nothing) which means this is mostly of moderate interest unless there is a K to FD adapter with aperture control.

I'm not aware of any Pentax K to Canon FD adapters. I think it might be impossible because the adapter would need to be extremely thin. Even Nikon F to Canon FD adapters are very flimsy.

And yes, you'll still need an adapter with aperture control for your DA and newer D-FA lenses.

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I can't find a K to FD currently for sale but they were made at one time not too long ago per some threads I have read. I can't recall the brand right now. The Nikon F mount and Pentax are essentially almost the same distance. I have mounted Nikon F lenses to my Pentax directly (no adapter) and taken pictures with that combo. However I see the wisdom in not over complicating things.

I can't find a K to FD currently for sale but they were made at one time not too long ago per some threads I have read. I can't recall the brand right now. The Nikon F mount and Pentax are essentially almost the same distance. I have mounted Nikon F lenses to my Pentax directly (no adapter) and taken pictures with that combo. However I see the wisdom in not over complicating things.

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The difference in flange distance between Pentax K and Nikon F is 1mm (it's 45.5 mm for the K mount and 46.5mm for the F mount). the mounts themselves are indeed very similar, and it's actually quite possible to use Nikon F lenses on Pentax cameras without any adapters (the lenses will focus past infinity), but it's not true for Pentax lenses on Nikon cameras.

I still own the DA 16-45 and two old DA kit zooms. Frankly, they just aren't much fun converted to M43 with a K-adapter with the aperture lever, being plastic lenses with hardly any resistance on the focus ring. The aperture mechanism has no mechanism to determine f-stp. You only know for sure wide open or full stop. The in-between settings are unknown. Of course, it doesn't matter because you would not remember the f-stops later. Perhaps, if I owned DA limited lenses I would feel differently, but if I did, I might still be shooting a Pentax DSLR.

I also have a 50mm f2 SMC lenses, so I have a PK-M43 adapter for it. I buy adapters for $10-12. The above K-adapter and this SMC-adapter do the job, but they are cheap.

Suggest that you just prioritize which lenses might make sense for usage on your GX7, and start with one adapter type. Figure out if you like manual focus, etc.

My most used legacy lenses are FD. I do have an M42-FD ring which allows me to put my Takumar screw mounts into an FD adapter. It and the Nikon-FD ring I had were both well made.

However, adapters are so inexpensive, it's just better to buy a dedicated adapter for a lens you use often. In the dark, it's hard enough to change lenses, much less attach an FD lenses to the fiddly FD adapters, so I added an extra one. No big deal at $12.

It's a different story with focal reducers. Even the cheap ones are not cheap, so I understand how you might want one to serve several mounts. In that case, EF will fit more lenses, except it won't take FD. A whole different thread is needed to debate the merits or value of focal reducers anyway, especially the inexpensive models.

FD mount hasn't been made for a long while so there's not much demand for adapters going to FD.
I use several EOS mount adapters, even though I have no EOS lenses. (Most of mine are PK, & M42 but I have an OM as well.)
I now have an extending helicoid adapter, a tilt adapter & a focal reducer all in EOS, and can use EOS-PK or EOS-OM adapters to mount my lenses on them. The EOS-lens adapters do tend to be much smaller making it more convenient to carry a variety. If I had any Nikon lenses I'm sure I'd find several EOS-F adapters without any problem. - This approach does not allow aperture control of the DA lenses, I have a standard DA adapter for that but don't really get on with the aperture control it gives so tend to stick to older PK glass for adapting.

The only issues I've had using adapters is short focal lengths - when trying lenses shorter than ~25mm the length of the adapter starts becoming critical...

Those are all very helpful replies.
I continue to shoot Pentax, and have an embarrassingly nice collection of lenses - some of which do not have aperture rings. I also have a very nice FD 85mm f1.8 SSC lens. My only Nikon glass is not great, so I really only need two basic adapters. Focal reducers aren't as big of a requirement right now.

Having a few Nikon adapters and a Nikon focal reducer I got a m42 -> Nikon to mount a Super Takumar. Obviously it works. I did not test infinity focus as I do not use it much but more adapters means more jiggle and more tolerance errors even if these could even cancel each other out giving a perfect result.
I think it's an option especially for expensive adapters or if you have just one different lens. Otherwise I see little value over specific adapters: the price of a cheap m42->micro43 and a m42->Nikon is about the same.

Having a few Nikon adapters and a Nikon focal reducer I got a m42 -> Nikon to mount a Super Takumar. Obviously it works. I did not test infinity focus as I do not use it much but more adapters means more jiggle and more tolerance errors even if these could even cancel each other out giving a perfect result.
I think it's an option especially for expensive adapters or if you have just one different lens. Otherwise I see little value over specific adapters: the price of a cheap m42->micro43 and a m42->Nikon is about the same.

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Mounting M42 lenses on Nikon bodies requires a optical element or infinity is lost. Nikon's F mount has a rear flange distance about 1mm more than PK & M42, or about 2mm more than EOS... For macro it doesn't matter but it's enough to prevent anything else being focused with wider lenses. IIRC it's the least adaptable of the 35mm SLR mounts.

I continue to shoot Pentax, and have an embarrassingly nice collection of lenses - some of which do not have aperture rings. I also have a very nice FD 85mm f1.8 SSC lens. My only Nikon glass is not great, so I really only need two basic adapters.

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I think that's a good strategy. I also think that you may perhaps benefit from buying one or two more adapters for your pentax lenses (depending how many you currently have that is) so that you can just leave the adapter on the lens. Get some cheapie m43 lens base caps so you can feel comfortable to carry them in your bag that way too.

Mounting M42 lenses on Nikon bodies requires a optical element or infinity is lost. Nikon's F mount has a rear flange distance about 1mm more than PK & M42, or about 2mm more than EOS... For macro it doesn't matter but it's enough to prevent anything else being focused with wider lenses. IIRC it's the least adaptable of the 35mm SLR mounts.

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I think you are right. The fact is that first I got a m42->micro43 adapter, then the m42->Nikon to use the focal reducer. I did not check the flange distances: usually you can find only the adapters that makes sense and the m42->Nikon were quite common on ebay.
Then probably I never actually used the last combo for real shots. I tried it this morning: with the normal adapter I can focus up to about 30 meters. With the focal reducer (Roxsen) I get up to 60-100 meters.

Anyway I was not suggesting to use Nikon as a "base" that as you say is the worst one.

Have an adapter for each slot in your camera bag. If you can field 4 pentax lenses during an outing, have 4 pentax adapters.

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I found that until you are swapping lenses of the same type there is no real advantage in having more then one adapter: to swap lenses you just leave the adapter on the camera and change the lens only. If you have some native and some Pentax then yes, more then one adapter may help.

I found that until you are swapping lenses of the same type there is no real advantage in having more then one adapter: to swap lenses you just leave the adapter on the camera and change the lens only.

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of course if you happen to also have a native lens (which was actually my first lens which came with my G1: a 14-45) then that gets old fast as I usually am swapping one lens for another. So if you ONLY have (say) Pentax lenses and no natives then maybe ... but then you'll need a body cap for that (unless you want to leave the sensor open).